Casein phosphopeptides (CPP) which develop in Grana Padano cheese
at
different ages were isolated by precipitation with Ba2+
and analysed by HPLC.
Profiles were complex throughout the period between 4 and 38 months. CPP
in a
cheese sample 14 months old were identified by a combination of fast atom
bombardment–mass spectrometry and Edman degradation. They were found
to
consist of a mixture of components derived from three parent peptides,
β-CNf(7–28)4P, αs1-CNf(61–79)4P and
αs1-CNf(7–21)4P. In total, 45 phosphopeptides
were identified: 24 from β-CN, 16 from αs1-CN and
5 from
αs2-CN. The presence of
aminopeptidase activity during cheese ripening was deduced from the presence
of a
number of CPP of different lengths with the loss of one or more residues
from
the N-terminus. The longest had C-terminal lysine and seemed to be progressively
hydrolysed by carboxypeptidases A and B to shorter peptides. CPP in cheese
appeared to be shortened plasmin-mediated products. Moreover, those most
resistant
to further hydrolysis contained at least three closely located phosphoserine
residues. The anticariogenic activity of CPP is also discussed.